I believe you have taken off the chute deflectors on all your JD 7 Iron decks, right?
I have a 717A, 7 Iron (not II). Yes, I like the 7 Iron deck as you. But, I have found that using the chute deflector is important for better cover of debris dispersal. In early Spring, and late Fall, the chute is fully down. This provides a more directed flow of material, less spray. When the grass is heavy, I raise up the end a couple of inches. It helps spread heavy clippings better when in that position.
I need to raise the chute for trailer transport. I have a light chain attached to the height adjustment control, running down to the end of the chute (bolt with large fender washers). I have an S-hook at the top. When I need to raise the chute for transport, the chute comes up, the hook finds the best link. During the use when I want to raise the end a couple of inches, I raise it, finding the best link for the S-hook.
In my experience (I'm working in SW PA), having the chute fully raised (equivalent to taking it off), I will have slight windrows about 3-6 feet from the discharge. Having it fully down, I get a wider dispersal, starting at about 2 feet, extending to 6-8 feet away. I see less windrowing with it fully down (unless the growth is heavy, then I raise the end a couple of inches as noted above).
Just my $0.02 from experience with the 7 Iron deck.
I only use mine part time, a bit more than 1,800 hours in five seasons.